Spark duration for capacitor discharge ignition systems

ABSTRACT

A capacitor discharge ignition system wherein an energy storage capacitor is charged to a relatively high voltage and synchronously discharged into the primary winding of an ignition coil to develop a high-energy short-time duration spark discharge at the secondary winding of the ignition coil, and a circuit is provided for increasing the time duration of the spark discharge beyond that normally obtained from the capacitor discharge system to improve the fuel-igniting properties of the spark.

United States Patent Inventor Gunter G. Schuette Addison, I11. Appl. No.888,782 Filed Dec. 29, 1969 Patented June 15, I971 Assignee MotorolaInc.

Franklin Park, Ill.

SPARK DURATION FOR CAPACITOR DISCHARGE IGNITION SYSTEMS 7 Claims, 4Drawing Figs.

U.S. Cl 315/244, 315/206, 317/96, 320/1, 307/106 Int. Cl 1105b 41/14Field of Search 317/79, 80, 96;315/183, 187, 200, 206, 209, 241, 244,289; 307/106; 320/1 [56] References Cited UNITED STATES PATENTS2,799,809 7/1957 Lautenberger 317/79 3,045,148 7/1962 McNulty et al.315/183 3,255,366 6/1966 McNulty et a1. 307/106 3,336,506 8/1967 Frank317/96 3,417,306 12/1968 Knak 320/1 3,457,456 7/1969 Dietz 315/206Primary Examiner-Velodymyr Y. Mayewsky Attorney-Mueller, Aichele &Rauner ABSTRACT: A capacitor discharge ignition system wherein an energystorage capacitor is charged to a relatively high voltage andsynchronously discharged into the primary winding of an ignition coil todevelop a high-energy short-time duration spark discharge at thesecondary winding of the ignition coil, and a circuit is provided forincreasing the time duration of the spark discharge beyond that normallyobtained from the capacitor discharge system to improve thefuel-igniting properties of the spark.

PATENTEUJUNISIH?! 35 4,5329

SHEET 1 [IF 2 UNCONTROLLED DISC HARGED FIGZ CONTROLLED DISCHARGEINVENTOR GUNTER G. SCHUETTE 441M WW ATTORN EYS.

SPARK DURATION FOR CAPACITOR DISCHARGE IGNITION SYSTEMS BACKGROUND OFTHE INVENTION This invention relates generally to ignition systems ofthe type producing a high-voltage low-current energy pulse at theprimary winding of an ignition coil, and more particularly to animproved capacitor discharge ignition system.

Capacitor discharge ignition systems, that is, systems which utilizecapacitors for intermittently discharging a relatively high-voltageenergy pulse through the primary winding of an ignition coil, have foundrelatively widespread and popular use in connection with internalcombustion engines. Such capacitor discharge ignition systems haveseveral advantages over conventional Kettering ignition systems. Oneadvantage is that the power drain from the automobile battery issubstantially reduced when using a capacitor discharge ignition system.Another advantage of capacitor discharge ignition systems is that aspark of higher voltage, i.e., higher fuel-igniting properties, can begenerated more readily with a somewhat rundown storage battery connectedthereto, than .could otherwise be obtained by a conventional ignitionsystem. Yet another advantage obtained from capacitor discharge ignitionsystems is that the spark potential generated at spaced-apart electrodeswithin a spark plug remains substantially constant over a much widerrange of engine speeds than otherwise can be obtained from theconventional ignition 1 systems.

Although capacitor discharge ignition systems have improved operatingcharacteristics, they produce a spark discharge having a time durationmuch less than that produced by a conventional Kettering ignitionsystem. Despite the fact that the voltage of the spark discharge issubstantially increased, and remains so over a much wider range ofengine speeds, it has been found that the fuel-igniting properties ofthe high-voltage short-duration spark discharge is somewhat limitedunder certain conditions. For example, although fuelair mixtures of theproper ratio are readily ignited in a reliable and repeatable fashionfrom the spark discharge of a capacitor discharge ignition system andthe high-voltage spark generally has sufficient fuel-igniting propertiesto ignite fuel mixtures which are slightly off the desired fuel-airmixture ratio, the fact is with a substantial abnormality of the desiredfuel-air mixture the capacitor discharge ignition systems heretoforeprovided may have difficulty in initiating combustion of the fuel-airmixture within a given cylinder of an internal combustion engine. Also,because of the short duration of the spark discharge produced bycapacitor discharge ignition systems, it is generally an importantrequirement that the proper air-fuel mixture withinthe cylinder of theengine be located substantially in the vicinity of the spaced-apartelectrodes of the spark plug so that the spark discharge will heat andignite the fuel mixture in this vicinity. However, the random mobilityof a given quantity of molecules of a fuel-air mixture may cause thevicinity around the spaced-apart electrodes to be vacant of sufficientfuel-air mixture during the short-duration spark discharge, this problembeing particularly acute in cold weather.

SUMMARY OF THE lNVENTlON It is therefore an object of this invention toprovide a capacitor discharge ignition system which overcomes theproblems set forth hereinabove, and which is efficient and reliable inoperation and inexpensive to manufacture.

Another object of this invention is to provide a capacitor dischargeignition system which will create a high-voltage spark discharge atspaced-apart electrodes for an increased time duration.

Briefly, the capacitor discharge ignition system of the illustratedembodiment includes a storage capacitor for receiving and storing ahigh-voltage energy pulse which is to be discharged into the primarywinding of an ignition coil in synchronism with external pulse signalinformation. The external pulse signal information may be generated by,for example, the opening of a mechanical breaker-point assembly, anelectrical impulse developed by a light-emitting pulsating source. Anenergy supply circuit is coupled to the energy storage capacitor todeliver thereto a high-voltage electrical energy pulse substantiallyimmediately after a previous energy pulse has been discharged from thecapacitor through the primary winding of the ignition coil. Thedischarge of the energy storage capacitor is accomplished by aseries-connected current control device, such as a silicon-controlledrectifier, which serves as a fast-acting switch. Most advantageously,means are provided in circuit with the current control device andarranged for connection to the primary winding of the ignition coil toprovide a sustained energy transfer condition at the primary winding or,in the alternative, to provide additional energy thereto. That is, themeans connected in circuit with the current control device is effectivesubstantially immediately in response to the discharge of the energystorage capacitor to extend the duration of the current flow through theprimary winding of the ignition coil beyond that of the normal timeduration. This action increases the time duration of the spark dischargeat the secondary winding of the ignition coil to greatly improve thespark-igniting properties of the spark discharge which, in turn, willenhance the starting capability ofan internal combustion engine.

In one embodiment of this invention an inductor is placed in seriesbetween the current control device, which discharges the energy storagecapacitor, and the primary winding of the ignition coil. The inductancevalue of the inductor is selected so that when combined with theinductance value of the primary winding of the ignition coil the totalinductance thereof will provide an inductive reactance preferablyapproximately equal to the capacitive reactance of the energy storagecapacitor for a given frequency. The time duration of one-half cycle ofthis given frequency is then selected to be the approximate timeduration of an energizing current pulse through the primary winding ofthe ignition coil and, because of the tight coupling of the ignitioncoil between its primary and secondary windings, is also the approximatetime duration of the spark discharge produced at the secondary winding.It should be understood that the inductive reactance is to be determinedduring the spark discharge at the secondary winding of the ignition coiland not during conditions of no spark discharge. Therefore, only duringthe spark discharge at the spaced-apart electrodes will the energystorage capacitor, and the inductance offered by the primary winding ofthe ignition coil, and the added inductance connected in seriestherewith, act as a resonant circuit substantially to increase the timeduration of the spark discharge. This increased time duration of thespark discharge will have a desirable affect on the startingcapabilities of an internal combustion engine.

In another embodiment of the illustrated invention means are provided toapply additional current flow through the primary winding of theignition-coil to commence substantially immediately after the dischargeof the energy storage capacitor or upon substantial discharge thereof.This additional current flow causes an aiding magnetic field to bedeveloped within the ignition coil during the period of time when aspark discharge is established across the spaced-apart electrodes of aspark plug. This additional current flow will establish a sparkdischarge for a period of time similar to that provided by adding anadditional inductance in series with the primary winding of the ignitioncoil, as mentioned hereinabove. Preferably, the additional current flowto the primary winding of the ignition coil is provided by a currentcontrol device which is triggered to its low-resistancecurrent-conducting condition in response to the discharge of the energystorage capacitor. The current control device remains conductive untilthe energy storage capacitor is again being charged with a subsequentenergy pulse in readiness to again be discharged into the primarywinding of the ignition coil.

Most advantageously, the current control device is a siliconcontrolledrectifier having its gate electrode connected to its anode through aresistor of a given predetermined resistance value which is selected tocause firing of the silicon-controlled rectifier at the precise momentin time. When the circuit arrangement of this inventionis used inconjunction with a capacitor discharge ignition system which utilizes asingle swing-blocking oscillator to apply energy pulses to the energystorage capacitor, the silicon-controlled rectifier which supplies theadditional current to the primary winding of the ignition coil iscommutated to an off condition by a reversal of voltage which isgenerated within the single swing-blocking oscillator. However, it willbe understood that the broad and novel conceptsof this invention can beused in connection with capacitor discharge ignition systems of variouskinds and that commutation to an off condition of the silicon controlledrectifier which supplies the additional current can be accomplished byany suitable and well-known means.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showingthe essential portions of a capacitor discharge circuit illustrating oneembodiment of this invention;

FIG. 2 is a graphical representation of a high-voltage spark dischargegenerated at the spaced-apart electrodes of FIG. 1 showing both theuncontrolled short duration discharge of a conventional capacitordischarge ignition system and an extended, controlled discharge of thecapacitor discharge ignition system incorporating the features of thisinvention;

FIG. 3 is a schematic diagram illustrating still another embodiment ofthis invention wherein means are provided for applying additionalcurrent through the primary winding of the spark coil substantiallyimmediately after the rapid discharge of the energy storage capacitor;

FIG. 4.illustrates a series of waveforms at various circuit pointswithin the circuit of FIG. 3.

. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. I thereis seen the essential portion of the capacitor discharge circuitrequired for a complete understanding of the present invention, anddesignated generally by reference numeral 10. Here, an energy storagecapacitor 12 is connected across a secondary winding 14a of atransformer 14, the other windings thereof not being shown and are ofany suitable configuration. Connected in series with the capacitor 12and secondary winding 14a is a diode 16 which serves to provide ablocking element in series with the capacitor 12 and secondary winding14a so that the charge on capacitor 12 remains until discharged into aprimary winding 18a of an ignition coil 18. The energy pulse oncapacitor 12 is delivered to the primary winding 18a through a currentcontrol device, here illustrated as the silicon-controlled rectifier 20,whichacts as a switch in response to external pulse signal informationapplied to a pulse-forming transformer 22.

Most advantageously, an inductance element 24 is connected in serieswith the silicon-controlled rectifier 20 and the primary winding 18a ofthe ignition coil 18 and serves to extend the time duration of a sparkdischarge developed between spaced-apart electrodes 26, which may be thespark gap in one or more spark plugs of an internal combustion engine.The high-voltage spark discharge at the spark gap 26 is deliveredthereto by a secondary winding 18b of the ignition coil 18. Upondischarge of capacitor 12 a slight current flow will pass through adiode 28 which has its cathode connected to the juncture of capacitor 12and diode 16, in a well-known manner.

The inductance value of the inductance element 24 is preferably selectedso as to assist in sustaining current flow through the primary winding18a ofthe ignition coil 18 during the period of time when a sparkdischarge exists between the spaced-apart electrodes 26. Preferably, theinductance value of the inductance element 24 is selected so that whenadded with the inductance value of the primary winding 180 they combineto provide an inductive reactance approximately equal to the capacitivereactance of the energy storage capacitor 12 at a given frequency; Thisprovides a resonant circuit between capacitor 12, inductance element 24and primary winding 18a during the period of time when thesilicon-controlled rectifier 20 is conductive and a spark discharge hasbeen initiated between the spaced-apart electrodes 26. In onearrangement it was found that an inductance value of 30 millihenrlesprovided good results when used with an Ignition coll having a primarywinding Inductance of approximately 9.3 millihenries. The improved sparkduration is best illustrated in FIG. 2 wherein the short-durationuncontrolled spark discharge obtained from a conventional capacitordischarge ignition system is designated by reference numeral 26a, andthe increased duration controlled spark discharge obtained from thecircuit of FIG. 1 is designated by reference numeral 26b.

To prevent ringing oscillations within the primary winding 18a a diode30 is connected in parallel with the primary winding and the inductanceelement 24, this diode being rendered conductive upon the reversal ofvoltage across the inductance element 24 and the primary winding 18a. Aprotection device 32 is connected in parallel with the diode 30 andserves to prevent reverse voltage breakdown of the diode 30. Theprotection device 32 preferably is a bidirectional thresholdersswitchingdevice, but it may be any suitable voltage-dependent resistance elementhaving a characteristic which will prevent excess voltage from appearingacross the diode 30.

Referring now to FIG. 3 there is seen an alternate arrangement of thisinvention wherein the spark duration at the spaced-apart electrodes 26is sustained beyond that normally obtained from a capacitor dischargeignition system by providing additional current flow through the primarywinding 18a by means of a current duration circuit 40. Preferably, thecur- 'rent duration circuit 40 comprises a current control device,

such as a silicon-controlled rectifier 42, which has its gate electrode42a connected to its anode 42b by means of a resistor 44. The resistancevalue of the resistor 44 is selected to cause the silicon-controlledrectifier 42 to be rendered conductive at a point in time substantiallyimmediately following the discharge of capacitor 12 into the primarywinding 18a of the ignition coil 18. It should be noted that in thisembodiment the inductance element 24 may be eliminated.

Battery potential, for example, that provided by the battery of anautomobile, is applied to a circuit point 46 and to the anode 42b of thesilicon-controlled rectifier 42 through a power-switching transistor 48which forms a single swingblocking oscillator with the transformer 14.The emitter electrode of transistor 48 is also connected to a pair ofprimary windings 14b and 140 of the transformer 14 which form a stepuptransformer with respect to the secondarywinding 14a, and primarywinding 140 also serves as a feedback loop to the base electrode oftransistor 48 through a parallel network including a resistor 50 and adiode 52 connected in series with another resistor54. The feedbacknetwork from primary winding 14c serves as a regenerative feedback loopto cause transistor 48 rapidly to become conductive to a saturatedcondition to apply a current pulse to the primary winding 14b and uponsensing a reduction of the rate of change of the magnetic field withinthe transformer 14 also serves rapidly to render a transistor 48nonconductive. The single swing blocking oscillator formed by transistor48 and transformer 14 applies an energy pulse to the energy storagecapacitor 12 which is then discharged into the primary winding 18a oftheignition coil 18 by means of the silicon-controlled rectifier 20. Asseen in FIG. 4, the curve 60 represents the emitter voltage oftransistor 48 as taken from the circuit point connected to the primarywindings 14b and Me of the transformer 14. At the point in time t,transistor 48 is rendered conductive as indicated by reference numeral600. This point in time corresponds to the discharge of capacitor 12 asindicated by the energy pulse applied to the primary winding 18a and isillustrated by the curve 62 which is a high-voltage pulse rapidlydecreasing to a slight depression 620 within the curve 62. It is thisdischarge of the capacitor 12 which causes transistor 48 to be renderedconducive as illustrated by the curve 60. However, it will be noted thatconduction of transistor 48 also applies battery potential to the anode42b of the silicon-controlled rectifier 42 to apply additional currentthrough the primary winding 18a as illustrated by the linear portion 62bof FIG. 4. The regenerative cutoff voltage developed in transformer 14is applied to the emitter electrode of transistor 48, as indicated bythe curved portion 60b of FIG. 4 to render transistor 48 nonconductivewhich, in turn, removes the battery potential from the siliconcontrolledrectifier 42 to terminate the additional current flow through primarywinding 18a, as indicated by .the rapid cutoff portion 62c of the curve62.

Here, the spark discharge between the spaced-apart electrode 26 isillustrated by the curve 64. A slight ringing action indicated by theseries of curves 6411- which are contiguous with the curve 64 representthe tendency of the ignition coil 18 to cause diminishing of the sparkdischarge duration along the dotted curve 66, which indicates the normaldischarge path of a conventional capacitor discharge ignition system.However, because of the added current flow through the primary winding18a which is transformer coupled to the secondary winding at a point intime when a spark discharge is already established, the short-durationpulse which would ordinarily occur, as indicated by the dotted curve 66,is extended into a long-duration pulse indicted by the curve 64,

and the advantageous results of this invention are obtained.

FIG. 3 also illustrates a diode 68 connected in parallel with theprimary winding of the pulse-forming transformer 22 which serves toreduce kickback voltage from occurring in the transformer, and aresistor 70 is connected in series with the primary winding-of the pulsetransformer 22 to apply the operating potential thereto when abreaker-point assembly, no shown, is in the closed circuit condition.The opening of the breaker-point assembly applies a trigger pulse to thegate cathode circuit of silicon-controlled rectifier in a conventionaland well-known manner to render the same conductive. Accordingly, whenusing either of the illustrated embodiments disclosed herein, the novelconcepts of this invention provide means for substantially increasingthe time duration of a spark discharge created between spaced-apartelectrodes when such spark is generated from a capacitor dischargeignition system. lclaim: l. A capacitor discharge ignition system forgenerating spark-producing potentials at the primary winding of anignition coil so that a spark discharge is produced between electrodesconnected to the secondary winding thereof, comprismg:

an energy storage capacitor for receiving and storing a highvoltageelectrical energy pulse; an energy supply circuit coupled to said energystorage capacitor for delivering thereto a high-voltage electricalenergy pulse substantially immediately after a previous energy pulse hasbeen discharged therefrom and applied to the primary winding of theignition coil;

control-switching means connected to said energy storage capacitor andarranged for connection to the primary winding of the ignition coil;

external pulse signal information means coupled to saidcontrol-switching means to render the same conductive in responsethereto substantially instantaneously to discharge said energy storagecapacitor into the primary winding of the ignition coil within arelatively short predetermined time interval to initiate a sparkdischarge between the electrode connected to the secondary winding; and

means connected in circuit with said control-switching means andarranged for connection to the primary winding of the ignition coil,said means being substantially immediately responsive to the dischargeof said energy storage capacitor to extend the duration of current flowthrough the primary winding of the ignition coil beyond that of saidrelatively short predetermined time interval to increase the duration ofthe spark discharge produced between the electrodes connected to thesecondary winding thereof. 7

2. The capacitor discharge ignition system of claim I wherein said meansis an inductance element connected in series between said controlswitching means and the primary winding ofthe ignition coil.

3. The capacitor discharge ignition system of claim 1 wherein said meansis an inductance element connected in series with said control-switchingmeans and the primary winding of the ignition coil, said inductanceelement having an inductance value such that when added to theinductance value of the primary winding ignition coil as provided duringthe spark discharge at the secondary winding thereof provides aninductive reactance substantially equal to the capacitive reactanceprovided by said energy storage capacitor for a given frequency.

4. The capacitor discharge ignition system of a 1 wherein said meansincludes a current control device connected in circuit with the primarywinding of the ignition coil, said current control device being renderedconductive upon discharge of said energy storage capacitor into theprimary winding of the ignition coil to supply added current flowthrough the winding winding after a spark discharge ignition beenestablished between the electrodes connected to the secondary winding ofthe ignition coil, said additional current flow continuing for apredetermined period of time to extend the time duration of the sparkdischarge between the electrodes beyond that normally obtained from aconventional capacitor discharge ignition system.

5. The capacitor discharge ignition system of claim 4 wherein saidcurrent control device is a silicon-controlled rectifier which isrendered conductive in response to the discharge of said energy storagecapacitor.

6. The capacitor discharge ignition system of claim 5 wherein saidsilicon-controlled rectifier has its gate electrode connected to itsanode by a resistance element having a resistance value to causeconduction of the silicon-controlled rectifier at a preselected point intime at which said energy storage capacitor is substantially discharged.

7. The capacitor discharge ignition system of claim 1 wherein saidenergy supply circuit includes a single swingblocking oscillator havinga step-up transformer, the primary winding of said step-up transformerbeing connected to a power transistor which is rendered conductive uponsensing the discharge of said energy storage capacitor to apply asubsequent pulse of energy to said energy storage capacitor, and saidmeans includes a silicon-controlled rectifier connected between saidpower transitor and the primary winding of the ignition coil to applyadditional current through the primary winding substantially immediatelyfollowing the discharge of said energy storage capacitor and during anestablished spark discharge between the electrodes connected to thesecondary winding of the ignition coil, said additional current flowcausing an increase in the spark duration between the electrodes.

1. A capacitor discharge ignition system for generating sparkproducingpotentials at the primary winding of an ignition coil so that a sparkdischarge is produced between electrodes connected to the secondarywinding thereof, comprising: an energy storage capacitor for receivingand storing a highvoltage electrical energy pulse; an energy supplycircuit coupled to said energy storage capacitor for delivering theretoa high-voltage electrical energy pulse substantially immediately after aprevious energy pulse has been discharged therefrom and applied to theprimary winding of the ignition coil; control-switching means connectedto said energy storage capacitor and arranged for connection to theprimary winding of the ignition coil; external pulse signal informationmeans coupled to said controlswitching means to render the sameconductive in response thereto substantially instantaneously todischarge said energy storage capacitor into the primary winding of theignition coil within a relatively short predetermined time interval toinitiate a spark discharge between the electrode connected to thesecondary winding; and means connected in circuit with saidcontrol-switching means and arranged for connection to the primarywinding of the ignition coil, said means being substantially immediatelyresponsive to the discharge of said energy storage capacitor to extendthe duration of current flow through the primary winding of the ignitioncoil beyond that of said relatively short predetermined time interval toincrease the duration of the spark discharge produced between theelectrodes connected to the secondary winding thereof.
 2. The capacitordischarge ignition system of claim 1 wherein said means is an inductanceelement connected in series between said control switching means and theprimary winding of the ignition coil.
 3. The capacitor dischargeignition system of claim 1 wherein said means is an inductance elementconnected in series with said control-switching means and the primarywinding of the ignition coil, said inductance element having aninductance value such that when added to the inductance value of theprimary winding ignition coil as provided during the spark discharge atthe secondary winding thereof provides an inductive reactancesubstantially equal to the capacitive reactance provided by said energystorage capacitor for a given frequency.
 4. The capacitor dischargeignition system of a 1 wherein said means includes a current controldevice connected in circuit with the primary winding of the ignitioncoil, said current control device being rendered conductive upondischarge of said energy storage capacitor into the primary winding ofthe ignition coil to supply added current flow through the windingwinding after a spark discharge ignition been established between theelectrodes connected to the secondary winding of the ignition coil, saidadditional current flow continuing for a predetermined period of time toextend the time duration of the spark discharge between the electrodesbeyond that normally obtained from a conventional capacitor dischargeignition system.
 5. The capacitor discharge ignition system of claim 4wherein said current control device is a silicon-controlled rectifierwhich is rendered conduCtive in response to the discharge of said energystorage capacitor.
 6. The capacitor discharge ignition system of claim 5wherein said silicon-controlled rectifier has its gate electrodeconnected to its anode by a resistance element having a resistance valueto cause conduction of the silicon-controlled rectifier at a preselectedpoint in time at which said energy storage capacitor is substantiallydischarged.
 7. The capacitor discharge ignition system of claim 1wherein said energy supply circuit includes a single swing-blockingoscillator having a step-up transformer, the primary winding of saidstep-up transformer being connected to a power transistor which isrendered conductive upon sensing the discharge of said energy storagecapacitor to apply a subsequent pulse of energy to said energy storagecapacitor, and said means includes a silicon-controlled rectifierconnected between said power transitor and the primary winding of theignition coil to apply additional current through the primary windingsubstantially immediately following the discharge of said energy storagecapacitor and during an established spark discharge between theelectrodes connected to the secondary winding of the ignition coil, saidadditional current flow causing an increase in the spark durationbetween the electrodes.